A. Field of the Invention
This invention relates to prosthesis liner or socket having a seal at its distal end.
B. Related Art
With prostheses in general and leg prostheses in particular, a substantial effort is made to spread the retention force with which the prosthesis is attached to the involved residual limb over as large a surface as possible. So-called suction prostheses are especially advantageous in that respect, as they are sealed hermetically against the residual limb. When a force occurs tending to pull the prosthesis off the residual limb, a partial vacuum is produced which, in cooperation with the external atmospheric pressure, retains the prosthesis on the residual limb.
The suction socket presumes a positive air tight seal. When leaks arise, the partial vacuum at once disappears and the residual limb slips out of the socket.
It is clear on its face that such an event occuring with a leg prosthesis entails a dangerous fall. If the patient during walking loses the prosthesis, his/her step cannot be completed because the affected leg is suddenly shortened. Because walking/running is a dynamic process, the patient has no chance of stopping the step short.
Heretofore, one-hundred percent reliable air tight seals could not be assured. The residual limb volume changes with the patient's blood pressure, the temperature, and the like in such a way that a socket which is well-fitting and air tight one day may be poorly fitting and very loose another. The resulting consequence is the danger discussed above.
In order to safely preclude such danger, liners pulled over the residual limbs are used for prosthetic sockets, even those that are for above-knee use. At its distal end the liner is fitted with a locking adapter engaging a detent mechanism or the like of the prosthetic socket. In this configuration the liner is seated in an air tight manner on the residual limb and there is no danger of the residual limb slipping out of the liner. Moreover, on account of its intrinsic prestressing force, the liner is frictionally held against the residual limb. On the other hand the liner's elasticity results in strong narrowing at its distal end when tension is introduced at such end through the locking adapter. The result is a so-called milking effect.
It is important for comfort during wearing that the residual limb not be compressed when a tension is applied to the distal end. Such objective may be assured when the liner is inserted in the hard prosthetic socket in an air tight condition and is kept there by means of a partial vacuum.
Accordingly, those embodiments which involve both mechanical and hermetic attachment will be advantageous.
In another example, the liner should include assistance for inserting the liner into a socket. For that purpose the liner is fitted at its distal end with a cord which initially is threaded through an aperture at the prosthetic socket distal end. The patient forcefully pulls the cord through the aperture, such that the residual limb, seated in the liner, is pulled into the prosthetic socket. Thereupon the cord is secured on the outside of the prosthetic socket. In this kind of prosthesis, the prosthetic socket is retained against the residual limb substantially by friction in relation to the cord affixed on the outside of the prosthetic socket.